Injection molding valve gate system and activating mechanism

ABSTRACT

A valve gate system for an injection molding machine, having a valve gate unit configured to be in contact with a manifold of an injection molding machine for delivering a molten plastic flow from a hot runner system to an injection chamber. The valve gate unit has a valve pin for controlling the flow of the molten plastic from a hot runner system to an injection chamber and an activating unit coupled with the valve gate unit. The activating unit is configured to be mounted external to a mold unit that houses the injection chamber. In addition, the activating unit has an element that extends through the mold unit to engage the valve pin, so as to control the molten plastic flow from a runner system to an injection chamber.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 60/502,341, filed Sep. 12, 2003, the teachings of whichare incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to injection molding machines, and inparticular to valve gate systems for injection molding machines, andinjection molding machines having molds using valve-gate systems forcontrolling the injection of molten plastic into the mold chamber.

Valve-gate systems have the advantage of creating a clean, flush gatemark, when minimal vestige height is required on the molded part. Apartfrom a cosmetic viewpoint, larger orifices allowed by valve gatesprevent drooling, reduce shear heat and molded-in stress, provide easierfiling and reduce injection pressure. Valve-gates are typically part ofa larger unit (commonly referred to as “valve-gate unit”) that ismounted behind the gate area, in firm contact with the hot runner'smanifold. More issues regarding existing valve-gate unit designs areraised below.

While existing valve gate systems create quality gates on molded parts,they also suffer from certain shortcomings, as described below.

-   -   The valve pin or stem of a valve gate unit is actuated typically        by pneumatic or hydraulic systems, included in the body of the        valve-gate unit, which contributes to increase valve pin length.    -   Pneumatic or hydraulic actuating systems included in heated        valve-gate units are continuously subjected to high        temperatures, and therefore likely to suffer from problems        associated with thermal expansion.    -   Pneumatic or hydraulic actuating systems mounted behind the        manifold require cooling. If no cooling is available, they        generally will require regular maintenance checks (e.g., to        inspect and/or change o-rings, etc.), which adds to the overall        cost of the operation of the machine.    -   Presence of pneumatic or hydraulic systems in valve-gate units        may limit the use of back-to-back gating for stack molds. In        such cases, when using a single manifold, staggered placement of        gates may be required, resulting in increased projected area. It        is noted that back-to-back mounting can be achieved if using        multiple manifolds, but, in such cases, equalizing flow in all        runners (e.g., to avoid preferential flow) becomes an issue.    -   Many of the existing valve-gate systems have no form of        adjustment of the valve pin length. An adjustment of some sort        is typically necessary to bring the valve pin flush with        surrounding molding surface. Existing systems that have this        adjustment still require a fair amount of work, even with the        mold in the injection press, resulting in increased downtime.

There is therefore a need for an improved valve-gate unit that does notsuffer from these issues.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a valve gate system and an injectionmolding machine having such a valve gate system, where the activatingunit of the valve gate system is located in an unheated area of theinjection molding machine and where an element of the activating unitextends through the injection molding machine to engage and activate thevalve gate of the valve gate unit.

In one embodiment, the present invention provides a valve gate systemfor an injection molding machine, having a valve gate unit configured tobe in contact with a manifold of an injection molding machine fordelivering a molten plastic flow from a hot runner system to aninjection chamber. The valve gate unit has a valve pin for controllingthe flow of the molten plastic from a hot runner system to an injectionchamber and an activating unit coupled with the valve gate unit. Theactivating unit is configured to be mounted external to a mold unit thathouses the injection chamber. In addition, the activating unit has anelement that extends through the mold unit to engage the valve pin, soas to control the molten plastic flow from a runner system to aninjection chamber.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings. The drawings describedbelow are merely exemplary drawings of various embodiments of thepresent invention which should not limit the scope of the disclosure andclaims herein. One of ordinary skill would recognize many variations,alternatives, and modifications. These variations, alternatives, andmodifications are intended to be included within the scope of thepresent invention, which is described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary schematic diagram of one embodiment of a valvegate unit in accordance with the present invention shown as a part of asingle-face multi-cavity mold.

FIG. 2 is an exemplary schematic diagram showing an enlarged detail viewof the valve-gate unit of FIG. 1.

FIG. 3 is an exemplary schematic diagram of one embodiment of a valvegate unit and the activating unit in accordance with the presentinvention shown as a part of a single-face multi-cavity mold.

FIG. 4 is an exemplary schematic diagram showing an enlarged detail viewof the activating unit of FIG. 3.

FIG. 5 is an exemplary schematic diagram showing another enlarged detailview of the activating unit of FIG. 3.

FIGS. 6A and 6B are exemplary schematic diagrams showing additionaldetail views of the activating unit of FIG. 3.

FIG. 7A is an exemplary schematic diagram of a curved activating slot ofthe valve gate unit of FIG. 1.

FIG. 7B is an alternate exemplary schematic diagram of an activatingslot of the valve gate unit of FIG. 1.

FIGS. 8-9 are exemplary schematic diagrams showing engagement positionson the slot of FIG. 7A.

FIGS. 10A-B are exemplary schematic diagrams showing engagementpositions of the activating rod on the slot of FIG. 7A.

FIGS. 11-13 are exemplary schematic diagrams of alternate embodiments ofa valve gate unit in accordance with the present invention shown as apart of a single-face multi-cavity mold.

FIG. 14 is an exemplary side view schematic diagram of an alternateembodiment of a valve gate unit and the activating unit having amulti-piece activation bar in accordance with the present inventionshown as a part of a single-face multi-cavity mold.

FIG. 15 is an exemplary schematic diagram showing engagement positionsof the activating rod of FIG. 14. FIG. 15 shows the mold of FIG. 14opened, for example, for the removal of valve gate unit(s).

FIGS. 16-19 are exemplary detailed view schematic diagrams of themulti-piece activation bar of FIG. 14; with activating inserts andconnecting bars shown separated in a top view (FIG. 16); front view(FIG. 17) and assembled shown in top view (FIG. 18) and front view (FIG.19).

FIG. 20 is an exemplary detailed schematic diagram of a connection ofthe pieces of the multi-piece activation bar of FIG. 14.

FIG. 21 is an exemplary cross sectional diagram through a stack moldusing back-to-back gating.

FIG. 22A is an exemplary plan view diagram of a multi-cavity mold (seenfrom the parting line), shown with two activating units.

FIG. 22B is an alternate exemplary plan view diagram of a multi-cavitymold (seen from the parting line), shown with two activating units andusing a multi-piece activating bar.

FIG. 22C is an alternate plan view diagram of FIG. 22B, seen from anopposite end.

FIG. 23 is an exemplary side view diagram of a stack mold, shown fromthe side where the activating units are mounted.

FIGS. 24A-C are exemplary schematic diagrams showing a first alternateembodiment of the valve gate unit in accordance with the presentinvention.

FIGS. 25A-C show the embodiment of FIGS. 24A-C with the valve gateclosed.

FIGS. 26A-C are simplified views of the embodiment of FIGS. 24A-C, shownwith the valve gate open.

FIGS. 27A-C simplified views of simplified views of this embodiment,shown with the valve gate closed.

FIGS. 28A-C are exemplary schematic diagrams showing a second alternateembodiment of the valve gate unit in accordance with the presentinvention.

FIGS. 29A-C show the embodiment of FIGS. 28A-C with the valve gateclosed.

FIGS. 30A-C are simplified views of the embodiment of FIGS. 28A-C, withthe valve gate open.

FIGS. 31A-C are simplified views of the embodiment of FIGS. 28A-C, withthe valve gate closed.

FIGS. 32A-C are exemplary schematic diagrams showing a third alternateembodiment of the valve gate unit in accordance with the presentinvention.

FIGS. 33A-C show the embodiment of FIGS. 32A-C with the valve gateclosed.

FIGS. 34A-C are simplified views of the embodiment of FIGS. 32A-C, withthe valve gate open.

FIGS. 35A-C are simplified views of the embodiment of FIGS. 32A-C, withthe valve gate closed.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention, described herein, may be usedfor single cavity molds, as well as with multi-cavity (e.g., single-faceand stack) molds.

The embodiments of the present invention use a combination ofpneumatic-mechanical actuating system for the movement of the valve pin.The pneumatic component (e.g., pneumatic cylinder) of the actuatingsystem is brought outside the mold, leaving only mechanical componentsin the mold. The pneumatic cylinder runs cold, which helps protect itscomponents from heat expansion and extend the life of its seals (e.g.,o-rings). Also, maintenance checks and service are easier for cylinderslocated outside the mold, where they are easily accessible. Thepneumatic actuating component being removed from the valve-gate unit,enables the back-to-back mounting of valve-gate units for stack molds.

An embodiment of the valve-gate unit in accordance with the presentinvention is shown in FIG. 1 as part of a single-face multi-cavity mold.Such a mold typically includes the following items: a bottom plate 1,stripper plate 2, stripper rings 3 (secured to stripper plate 2), cores4 (secured to bottom plate 1), cavity blocks 5 secured to cavity plate6, gate inserts 7 (secured in cavity blocks 5), manifold plate 8,housing manifold 9, top plate 10, and valve-gate units 11 (secured tocavity plate 6). It should be understood that additional components (notshown or described here) can be part of such a mold, and differentmounting methods than the one described can be used, without departingfrom the scope of the present invention.

In a manner typical to the injection process, at the beginning of eachinjection cycle the mold closes and molten plastic is injected, throughthe hot runner system (e.g., as shown including a manifold 9 and anozzle unit 12), in the injection chambers 13 formed between the activefaces of cores 4 and cavity blocks 5. The active end of nozzle unit 12shown in FIG. 1 is housed in gate insert 7, but can be housed directlyin a pocket in cavity block 5 (e.g., gate insert 7 is optional). At theend of the injection cycle, the mold opens and the stripper plate 2moves away from bottom plate 1 for a short distance, causing thestripper rings 3 to strip the molded parts 14 off cores 4. The moldedparts 14 fall through the opening between the mold halves, and theinjection machine closes the mold for the beginning of a new cycle.

The valve-gate system in accordance with the embodiments of the presentinvention includes two main units: the valve-gate unit 11 (as shown inFIG. 1), secured to cavity plate 6 and in contact with manifold 9, andthe activating unit 31 (as shown in FIG. 3), mounted on the side of themold, and having elements that go through the mold, to valve-gate units11.

Melt-flow channels through manifold 9 bring molten plastic to valve-gateunits 11. Valve-gate units 11 can have one flow channel connecting tonozzle unit 12, or they can have two flow channels (e.g., as shown inFIG. 3), diverging from a common entry point (e.g., matching exitchannel of manifold 9), and converging at interface with nozzle unit 12.Sealing between manifold 9 and valve-gate unit 11, and betweenvalve-gate unit 11 and nozzle unit 12, is achieved by the thermalexpansion of these components. In single-face molds, pressure pads 78are mounted between manifold 9 and top plate 10, in line with the gate(one pressure pad for each injection point—e.g., see FIG. 1). Pressurepads 78 are used to counteract the injection pressure from the gate, andaid with sealing when components expand during mold cycles. In stackmolds with back-to-back gating, pressure pads may not be needed as theinjection pressures equalize on sides of manifold.

An enlarged detail of the valve-gate unit 11 from FIG. 1 is shown inFIG. 2. It includes a valve pin or stem 15 going through nozzle unit 12and through a central hole in the body of valve-gate unit 11. It has anenlarged cylindrical portion 16, followed by a reduced cylindrical end17. A flanged sleeve 18 is mounted on this end, followed by a retainer19, these two components being locked in place with a retaining ring 20.Although these items are employed and described in the present design,it should be understood that any system producing a similar result couldbe used on this end of valve pin 15. Flanged sleeve 18 and retainer 19move in a pocket 21 in the body of valve-gate unit 11. Pocket 21 isround on one side, and open to the other side, towards the exterior ofthe body of valve-gate unit 11. A yoke 22 is located in the open end ofpocket 21, pivoting around a pivot-pin 23 secured in the body ofvalve-gate unit 11. The forked end 24 of yoke 22 is located in the spacebetween flanged sleeve 18 and retainer 19 (mounted on reducedcylindrical end 17 of valve pin 15). Yoke 22 has a spherical end 25 onthe opposite side, which can move in a rounded slot/activating profile26 in an activating bar 27. A cover cap 28, bolted to body of valve-gateunit 11, acts as guide for activating bar 27. A thermal plate 29prevents heat transfer from body of valve-gate unit 11, which is heated,to activating bar 27 and cover cap 28. A cover plate 30 is bolted at topof valve-gate unit 11, to separate pocket 21 from manifold 9.

One activating bar 27 can be used to activate several valve-gate units11 located along the same axial line. The activating bar 27 extends toone side of the mold, where it is connected to the activating unit 31,as shown in FIG. 3. An enlarged detail of the activating unit 31 of FIG.3 is shown in FIG. 4. The activating unit 31 includes a base guide 32,an adjusting nut 33, an adjustable cylinder support 34 and a pneumaticcylinder 35. Base guide 32 is a round piece, extended with a squaredbase 36 that is secured to the side of the mold with bolts 37 (as shownin FIGS. 4, 5 and 6B). On the opposite end, base guide 32 has an outerthread 38, for engagement of adjusting nut 33. Base guide 32 has acentral cylindrical hole with one axial slot 39. Adjustable cylindersupport 34 is in the shape of a sleeve with a flanged end. A transversalkey 40 is press-fit in an axial slot 41 on the outer surface (on thesleeve portion) of adjustable cylinder support 34. Sleeve portion ofadjustable cylinder support 34 is inserted in central hole of base guide32, with transversal key 40 sliding in axial slot 39. Transversal key 40prevents rotation of adjustable cylinder support 34 in reference withbase guide 32. Adjustable cylinder support 34 is loosely secured toadjusting nut 33 with shoulder bolts 42. As shown in FIG. 6A, outersurface of adjusting nut 33 has a notched portion 43 (for ease ofhandling), extending with a narrow cylindrical portion 44, marked with anumber of indentations 45. One “origin” indentation 59 is marked on theouter surface of flange portion of adjustable cylinder support 34.Indentations 45 are used for precise adjustment in reference with“origin” indentation 59.

Pneumatic cylinder 35 is secured onto the end face of adjustablecylinder support 34 with bolts 46, as shown in FIG. 4. External end 48of piston 47 of pneumatic cylinder 35 has an internal thread 49. Aconnector 50, in the shape of a square prism, has a threaded extension51 at one end (for engagement in piston 47) and a central slot 52 at theother end (as shown in FIG. 5, which is a top view of system from FIG.4). End 53 of activating bar 27 is secured in central slot 52 with alow-head bolt 54. Four (4) access holes 55 are located, at 90°intervals, on middle portion of base guide 32, to provide access tolow-head bolt 54. Piston 47 of pneumatic cylinder 35 actuates connector50, which in turn directs activating bar 27 in a push-pull movement. Bar27 has one rounded slot/activating profile 26 for each valve-gate unit11 it activates. Activating slot 26 runs along a curve/spline 56 (asshown in FIGS. 3, 7A, 8, 9, 10, and 14), and holds the spherical end 25of yoke 22 previously described. Yoke 22 cannot move axially (in thedirection of movement of activating bar 27), as it is held in body ofvalve-gate unit 11, but can pivot around pivot pin 23. The push-pullmovement of activating bar 27 makes the rounded slot 26 guide thespherical end 25 of yoke 22 in an up-and-down movement, in a manner thatwill be described in more detail later. In other words, the up-and-downmovement of the spherical end 25 causes yoke 22 to pivot aroundpivot-pin 23, which makes the forked end 24 of yoke 22 move down-and-uprespectively, bringing the valve pin 15 with it. Valve pin 15 opens andclose once per injection cycle. The pneumatic cylinder 35 receives asignal from the injection machine, which correlates movement of valvepin 15 with mold cycles.

The 3 positions on curve 56 (as shown in FIG. 7A), are next described,with correlation to FIGS. 8, 9, 10A, and 10B. In the case describedhere, curve 56 is an arc (e.g., a portion of a circle).

-   -   Position “0” (zero), also shown in FIGS. 8 and 10A, corresponds        to valve-gate being closed (when injection is stopped). Piston        47, connector 50 and activating bar 27 are fully retracted (FIG.        10A), which corresponds to 0° rotation of yoke 22. In this        position, forked end 24 of yoke 22 is lowered, bringing valve        pin flush with surrounding surface of injection chamber 13.    -   Position “1”, also shown in FIGS. 9 and 10B, corresponds to        valve-gate being fully opened (when injection is in progress).        Piston 47, connector 50 and activating bar 27 are extended at        full stroke S (FIG. 10B), which corresponds to rotation “A” of        yoke 22. In this position, forked end 24 of yoke 22 is lifted at        maximum, retracting valve pin 15 by amount “B” (FIG. 9). Note:        Spherical end 25 of yoke 22 moves repeatedly from “0” to “1” and        back to “0” during mold cycles (once per mold cycle).    -   Position “2” is at the quadrant of curve 56 traveled by        spherical end 25 of yoke 22. Valve pin 15 can be adjusted to        move towards injection chamber 13 (to bring it flush with        surrounding surface, or to eliminate plastic leaks at gate,        etc.) by moving spherical end 25 of yoke 22 anywhere between “0”        and “2”. Quadrant “2” is the highest position the spherical end        25 can reach, and corresponds to the furthest out the valve pin        15 can go towards injection chamber 13. If spherical end 25 of        yoke 22 is at “2” and valve pin is below surrounding surface of        injection chamber 13, it cannot be adjusted any further and will        need to be replaced with a longer pin.

Stroke S is an in-built feature of pneumatic cylinder 35 used, and itsvalue is thus typically a constant. Values “A” and “B” are a result ofthe combination of stroke S of pneumatic cylinder 35 used, geometry ofcurve 56, and shape and size of yoke 22. These values can be varieddepending on desired result.

Procedure to adjust activating unit:

In order to adjust the activating unit, the following procedure may befollowed:

-   -   1. Mold is stopped.    -   2. Shoulder bolts 42 are loosened slightly (but not removed) to        allow a little clearance between adjustable cylinder support 34        and adjusting nut 33.    -   3. Adjusting nut 33 is rotated while adjustable cylinder support        34 is slowly pulled away from (or moved inward into) base guide        32, as shoulder bolts 42 bolted in adjusting nut 33 rotate in        annular groove 57 of adjustable cylinder support 34. This        movement increases or reduces adjustment gap 58 between front of        base guide 32 and flanged portion of adjustable cylinder support        34.    -   4. Indentations 45 of adjusting nut 33 help mold operator        control the adjustment precision in reference with the origin        indentation 59 of adjustable cylinder support 34.    -   5. When desired adjustment has been reached, shoulder bolts 42        are tightened, locking adjusting nut 33 and adjustable cylinder        support 34 together. When these two items are locked together,        they are also locked into position, in reference to base guide        32. This is achieved by the combination of transversal key 40        and thread 38. As transversal key 40 allows only axial movement        of adjustable cylinder support 34 in reference to base guide 32,        when shoulder bolts 42 are tightened, they also force the        threads of adjusting nut 33 against the opposing threads of base        guide 32, resulting in a solid, precise engagement of all the        components of activating unit 31.    -   6. Steps 2, 3, 4, and 5 are repeated for each activating unit 31        mounted on mold, depending on performance of valve pins 15.    -   7. Once all activating units 31 have been adjusted, the mold can        be started again.

A more detailed explanation of the correlation between adjustment onactivating unit 31 and location of spherical end 25 of yoke 22 on curve56 follows, in reference with FIGS. 7A, 7B, 8, 9, 10A and 10B. Position“1” is at the bottom of rounded slot/activating profile 26. Position “0”is located, along the length of the activating bar 27, at a distance,from “1”, equal to the stroke S of pneumatic cylinder 35. Position “2”is always at the quadrant of curve 56. When adjustment gap 58 is altered(unit 31 is being adjusted), adjusting nut 33, adjustable cylindersupport 34, and pneumatic cylinder 35 move relative to base guide 32,bringing connector 50 and activating bar 27 with them. This means thatadjustments modify location of position “0” relative to position “2” oncurve 56. Since distance, along length of activating bar 27, between “0”and “1” is constant (equal to stroke S of pneumatic cylinder 35),position “1” also moves with every adjustment. Valve pin 15 will need tobe replaced with a longer one when it requires adjustment beyondposition “2”.

A feature of curve 56 (of rounded slot/activating profile 26) thatinfluences the closing speed of valve pin 15 is discussed below, withreference to FIGS. 7A and 7B. When spherical end 25 of yoke 22 movesalong curve 56 from “1” to “0”, its speed decreases as the angle of thecurve reduces. This translates into the valve pin slowing down slightlyas it reaches the gate, allowing for a smooth closing. For comparisonpurposes, FIG. 7B shows a straight activating slot 26 (straight from “1”to “0”), which would result in a constant closing speed of the valve pin15.

For comparison purposes, FIG. 10A shows activating unit 31, completewith activating bar 27, in position “0”, while FIG. 10B (below it) showssame system in position “1”. Piston 47 is retracted in FIG. 10A,bringing spherical end 25 of yoke 22 in position “0”, and extended inFIG. 10B, bringing spherical end 25 in position “1”. Yoke 22 is shown atthe left of the figures for clarity.

One embodiment of this invention is directed to the use of a one-pieceactivating bar 27, the distance between activating slots 26 beingdetermined by the pitch of the mold. An alternate embodiment, however,uses a multi-piece activation bar (FIGS. 14, 15), where the activatingprofile 26 is part of an activating insert 60, made of high-wearmaterial. The mold pitch influences the length of connecting bars 61that connect activating inserts 60. As shown in FIGS. 16 through 20,slotted activating inserts 60 and connecting bars 61 have atongue-and-groove style joint 62, locked with a transversal key 63 ofsquare section. Transversal key 63 has a cylindrical extension 64 with agroove 65. A washer 66 and a retaining ring 67 (pushed in groove 65)lock the transversal key 63 in place, which in turn locks the slottedactivating inserts 60 in connecting bars 61 and in activating bar 27.Transversal key 63 has a knurled cylindrical flange 68 at opposite end,which is used for handling.

The multi-piece embodiment has several advantages in regards toservicing of the valve-gate unit. For a single-face mold (as shown inFIGS. 11, 12 and 13) the procedure to service the valve-gate unit is asfollows:

-   -   1. Mold is closed in the injection machine. Valve-gates must be        closed (pistons 47 of pneumatic cylinders 35 are fully        retracted).    -   2. Safety straps 69 are installed between top plate 10 and        cavity plate 6 (shown with phantom lines). Mold is opened and        bolts 70 are removed. Mold is closed again.    -   3. Safety straps 69 are then installed between cavity plate 6        and bottom plate 1.    -   4. Mold is opened slowly, as shown in FIG. 12, bringing cavity        plate 6, manifold plate 8 (which is secured to cavity plate 6),        and valve-gate units 11 (secured to cavity plate 6) with the        core half, away from cavity side.    -   5. Manifold 9 stays with top plate 10, as it is secured to top        plate 10 with bolts 71.    -   6. When mold is opened this way, valve-gate units 11 are exposed        and can be removed, one at a time, for service, cleaning etc. To        do that, bolts 72 (that secure valve-gate unit 11 to cavity        plate 6) can be removed, as shown in FIG. 13. Retaining rings 66        (see FIG. 20) are removed from grooves 65 of cylindrical        extensions 64, and transversal keys 63 are then removed. Slotted        activating insert 60 can then be easily disengaged from        connecting bars 61 (which will stay in the mold, attached to        adjacent valve-gate units) and valve-gate unit 11 (together with        its activating insert 60) can be lifted out of the mold, using        threaded portion of holes for bolts 72 as jacking holes 73.        After changes, cleaning, service etc. valve-gate unit 11 can be        returned to the mold and secured back in it, in reverse order.        Another valve-gate unit 11 can then be removed in the same        manner.

FIG. 14 shows a side view of a single-face multi-cavity mold, in closedposition, using a multi-piece activating bar 27. FIG. 15 shows same moldbeing opened in the manner described above, for removal of valve-gateunits 11. FIGS. 16 through 19 are detailed views of multi-pieceactivating bar 27, with activating inserts 60 and connecting bars 61shown separated in top view (FIG. 16) and front view (FIG. 17), andassembled (complete with transversal keys 63, washers 66, and retainingrings 64), shown in top view (FIG. 18) and front view (FIG. 19).

FIG. 21 shows a cross section through a stack mold using back-to-backgating. Valve-gate units 11 are shown, complete with activating bar 27(one-piece option shown) and activating units 31 mounted to side ofmold. Valve-gate units 11 are be heated, to hold desired temperature ofmolten plastic as it transits from manifold 9 to nozzle unit 12.Different types of heating elements 74 can be used (coil heaters wrappedaround body of valve-gate unit 11, or bar-type heaters inserted in thebody of the valve-gate unit 11 as shown in FIG. 21, etc.). Wires 75extending from heaters 74 are directed through pockets in the mold,similar with wires 76 coming from nozzle unit 12, and wires 77 comingfrom heaters of manifold 9.

FIG. 22A is a plan view of a multi-cavity mold (seen from the partingline), shown with two activating units 31. The two cavities at thebottom of the mold are shown with valve-gate open (one-piece activatingbar 27 is extended at full stroke S of pneumatic cylinder 35, as shownjust below the plan view). The two cavities at the top of the mold areshown with valve-gate closed (activating bar 27 is retracted fully, asshown above the plan view). At the right of the page, valve gate units,complete with nozzle units, are shown open (bottom) and closed (top),corresponding to plan view.

FIG. 22B shows the same mold in plan view, but using a multi-pieceactivating bar 27. FIG. 22C is a plan view of the same mold from FIG.22B, seen from opposite end—after top plate 10 and manifold 9 areremoved. The valve-gate units 11 and multi-piece activating bars 27 arevisible, and valve-gate units 11 can be removed, one by one, aspreviously described.

FIG. 23 is a side view of a stack mold, shown from the side where theactivating units 31 are mounted.

FIGS. 24A-C are exemplary schematic diagrams showing a first alternateembodiment of the valve gate unit in accordance with the presentinvention.

The embodiment of FIGS. 24A-C uses a pair of activating bars 27′ workingin parallel as a rigid unit. They can be of either one-piece ormulti-piece design, and are connected in a rigid assembly by means knownto those of skill in the art. An activating unit 31′, mounted externallyon the injection mold, activates both bars 27′ simultaneously. A pair ofbars 27′ may activate one or several valve gate units 11′ located alongthe same axial line. Cover caps 28′, secured to opposing sides of thebody of valve gate unit 11′, act as guides for activating bars 27′. Eachactivating bar has a slot/activating profile 26′ for each valve gateunit 11′ activated. This embodiment shows a linear, sloped slot, but itshould be understood that a rounded slot such as those described abovemay be used.

The valve gate unit 11′ of this embodiment has a round pocket 21′,disposed centrally, opening to the side which comes in contact withmanifold 9′. A cylindrical guide 80, in threaded engagement 81 with acylindrical cage 82, is located in round pocket 21′. A valve stem 15′has a cylindrical flange 83, located centrally in cage 82. Flange 83 isfirmly held between base of cage 82 and bottom of threaded extension ofguide 80, with no freedom of axial motion. Guide 80, flange 83 of valvestem 15′, and cage 82 form a sliding unit 84, which can move axially inpocket 21′ to repeatedly close or open a valve gate opening into aninjection chamber 13′ of the injection mold. Such motion of the slidingunit is achieved by a transversal pin 85, fixedly engaged in guide 80,and having symmetrical extensions on sides of guide 80. Ends oftransversal pin 85 pass through vertical slots 86 on sides of valve gateunit 11′, continuing on through activating profiles 26′, and beingsecured with some means such as retaining rings (as shown) againstaccidental sliding out of profiles 26′. With each extension of thepiston 47′ of a pneumatic cylinder 35′ of activating unit 31′, the pairof bars 27′ extends, causing the activating profiles 26′ to forcetransversal pins 85 to retract sliding units 84, so that valve stems 15′open the valve gates. With each retraction of the piston 47′, the pairof bars 27′ retracts, causing the activating profiles 26′ to forcetransversal pins 85 to extend sliding units 84, so that valve stems 15′close the valve gates. Vertical slots 86 only allow extend/retractmotions along axis of valve stem 15′, preventing any sideway motions ascould be caused by slots 26′ of activating bars 27′, acting againsttransversal pin 85. A cover plate 30′, secured at the top of the valvegate unit 11′, separates pocket 21′ from manifold 9′.

FIGS. 25A-C show the embodiment of FIGS. 24A-C with the valve gateclosed.

FIGS. 26A-C are simplified views of the embodiment of FIGS. 24A-C, shownwith the valve gate open.

FIGS. 27A-C simplified views of simplified views of this embodiment,shown with the valve gate closed.

FIGS. 28A-C are exemplary schematic diagrams showing a second alternateembodiment of the valve gate unit in accordance with the presentinvention.

The embodiment shown in FIGS. 28A-C uses a pair of activating bars 27′working in parallel as a rigid unit. They can be of either one-piece ormulti-piece design, and are connected in a rigid assembly by means knownto those skilled in the art. An activating unit 31′, mounted externallyon the injection mold, activates both bars 27′ simultaneously. A pair ofbars 27′ may activate one or several valve gate units 11′ located alongthe same axial line. Rollers 87 and support pads 88 guide theextend/retract motions of bars 27′, as activated by unit 31′. Activatingbars 27′ transfer this motion, through pins 89, to side arms 90, whichtransfer it further, through transversal pin 85′, to a sliding unit 84′(similar to the one described above). Vertical slots 86′ in oppositesides of valve gate unit 11′ allow extend/retract motions of pin 85′, asactivated by bars 27′. Such motions of pin 85′ are transferred directlyto valve stem 15′ through sliding unit 84′. When activating bars 27′ areextended, they cause side arms 90 to pull pin 85′ to the bottom end ofslots 86′. Pin 85′ brings the whole sliding unit 84′ down, which causesthe valve stem 15′ to close the valve gate as shown in FIGS. 29A, B, andC. When activating bars 27′ are retracted, they cause side arms 90 topush pin 85′ to the top end of slots 86′, bringing the whole slidingunit 84′ up, and causing the valve stem 15′ to open the valve gate (asshown in FIGS. 28A, B, and C).

FIGS. 29A-C show the embodiment of FIGS. 28A-C with the valve gateclosed.

FIGS. 30A-C are simplified views of the embodiment of FIGS. 28A-C, withthe valve gate open.

FIGS. 31A-C are simplified views of the embodiment of FIGS. 28A-C, withthe valve gate closed.

FIGS. 32A-C are exemplary schematic diagrams showing a third alternateembodiment of the valve gate unit in accordance with the presentinvention.

The embodiment shown in FIGS. 32A-C uses a pair of activating bars 27′working in parallel as a rigid unit. They can be of either one-piece ormulti-piece design, and are connected in a rigid assembly by means knownto those of skill in the art. An activating unit 31′, mounted externallyon the injection mold, activates both bars 27′ simultaneously. A pair ofbars 27′ may activate one or several valve gate units 11′ located alongthe same axial line. Roller bearings 91 guide the extend/retract motionsof bars 27′, as activated by unit 31′. Activating bars 27′ transfer thismotion, through a toggle system 92, to a transversal pin 85′, to asliding unit 84′ (similar to the one described above) and to a valvestem 15′. The toggle system 92 has of two side arms, 93 and 94, theirconnecting pins 95 and 96, and the transversal pin 85′. Pins 95 arefixedly secured onto opposite sides of the valve gate unit 11′. Pins 96connect side arms 93 and 94, and are allowed motion in vertical slots 97of activating bars 27′. Side arms 94 are further connected to ends oftransversal pin 85′. Vertical slots 86′ on opposite sides of valve gateunit 11′ only allow pin 85′ an extend/retract motion along axis of valvestem 15′. Such motions of pin 85′ are transferred directly to valve stem15′ through sliding unit 84′. When activating bars 27′ are extended,vertical slots 97 cause pins 96 to move simultaneously along horizontaldirection of activating bars 27′ and vertically towards bottom of slots97 (which are open at the top). Since side arms 93 can only pivot aroundpins 95 (when actuated by activating bars 27′), the resulting combinedhorizontal/vertical motion of pins 96 causes side arms 94 to pulltransversal pin 85′ to bottom end of vertical slots 86′. Pin 85′transfers this motion to the sliding unit 84′, causing the valve stem15′ to close the valve gate, as shown in FIGS. 33A, B, and C. Whenactivating bars 27′ are retracted, vertical slots 97 cause pins 96 tomove simultaneously along horizontal direction of activating bars 27′and vertically towards top of slots 97. Side arms 93 pivot around pins95, the resulting combined horizontal/vertical motion of pins 96 causesside arms 94 to push transversal pin 85′ to top end of vertical slots86′. Pin 85′ transfers this motion to the sliding unit 84′, causing thevalve stem 15′ to open the valve gate, as shown in FIGS. 32A, B, and C.

FIGS. 33A-C show the embodiment of FIGS. 32A-C with the valve gateclosed.

FIGS. 34A-C are simplified views of the embodiment of FIGS. 32A-C, withthe valve gate open.

FIGS. 35A-C are simplified views of the embodiment of FIGS. 32A-C, withthe valve gate closed.

It should be noted that in all three alternate embodiments describedabove, S1 is the stroke of the activating bars 27′, along a directionperpendicular to that of valve stem 15′. Sliding unit 84 and valve stem15′ have a stroke S2, along the centerline of the valve stem 15′. Bothstrokes are shown on FIGS. 24A, B and C of the first alternateembodiment. For the other two embodiments, however, only stroke S2 isshown, for clarity of the drawing. The two extreme positions of theseembodiments (when valve is open and when valve is closed) were not shownon the same drawing to avoid unnecessarily cluttering the figures.

As will be understood by those skilled in the art, the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. For example, instead of the pneumaticcylinder, a hydraulic one may be used may, or alternately the motiveforce may be supplied by an electric motor drive. These otherembodiments are intended to be included within the scope of the presentinvention, which is set forth in the following claims.

1. A valve gate system for an injection molding machine, comprising: avalve gate unit configured to be in contact with a manifold of aninjection molding machine for delivering a molten plastic flow from ahot runner system to an injection chamber, said valve gate unit having avalve pin for controlling the flow of the molten plastic from a hotrunner system to an injection chamber; and an activating unit coupledwith said valve gate unit, configured to be mounted external to a moldunit that houses the injection chamber, said activating unit having anelement that extends through the mold unit to engage said valve pin, soas to control the molten plastic flow from a runner system to aninjection chamber wherein said activating unit comprises one of apneumatic and a hydraulic cylinder, wherein the piston of said cylinderis configured to engage an activating bar of said element, saidactivating bar having a slot configured to engage one end of a yoke thatis held in the body of said valve gate unit, the other end of the yokeis configured to engage said valve pin, such that a push-pull movementof the piston causes a push-pull movement of the activating bar which inturn causes a down and up movement of said one end of said yoke, whichin turn causes an up and down movement of said valve pin, saidactivating bar comprising more than one section and an activating inserthaving a slot and a non-slotted connecting bar.
 2. The valve gate systemof claim 1 wherein said activating unit is configured to be housed in anon-heated region of an operating injection molding machine.
 3. Thevalve gate system of claim 1 wherein the piston of said cylinder isconfigured to engage an activating bar of said element, wherein saidactivating bar is in turn configured to engage said valve pin, such thata push-pull movement of the activating bar causes an up and downmovement of said valve pin.
 4. The valve gate system of claim 1 whereinsaid cylinder is configured to receive a signal from the injectionmolding machine to control the movement of said valve pin.
 5. The valvegate system of claim 1 wherein said valve gate unit is one of severalvalve gate units, each valve gate unit having a valve pin, and whereinsaid slot in said activating bar is one of several slots, each slotconfigured to engage one of said several valve pins.
 6. The valve gatesystem of claim 1 wherein the shape of said slot is configured tocontrol the travel speed of said valve pin.
 7. The valve gate system ofclaim 1 wherein said activating insert and said connecting bar areconfigured to be connected with one-another using a tongue and groovearrangement.
 8. The valve gate system of claim 1 wherein said activatingbar is a one-piece element.
 9. The valve gate system of claim 1 whereinsaid valve gate unit is placed in a back-to-back configuration withanother of said valve gate unit.
 10. An injection molding apparatus,comprising: a hot runner system having a manifold for delivering amolten plastic flow; an injection chamber for receiving the moltenplastic flow delivered from said hot runner system; a valve gate unit incontact with the manifold for delivering a molten plastic flow from saidhot runner system to said injection chamber, said valve gate unit beingpositioned entirely on one side of the manifold, said valve gate unithaving a valve pin for controlling the flow of the molten plastic fromsaid hot runner system to said injection chamber; and an adjustableactivating unit coupled with said valve gate unit, mounted external to amold unit that houses said injection chamber, said activating unithaving an element that extends through the mold unit to engage saidvalve pin to control the molten plastic flow from said hot runner systemto said injection chamber, said activating unit comprises one of apneumatic and a hydraulic cylinder, wherein the piston of said cylinderis configured to engage an activating bar of said element, saidactivating bar having a slot configured to engage one end of a yoke thatis held in the body of said valve gate unit, the other end of the yokeis configured to engage said valve pin, such that a push-pull movementof the piston causes a push-pull movement of the activating bar which inturn causes a down and up movement of said one end of said yoke, whichin turn causes an up and down movement of said valve pin.
 11. Theinjection molding apparatus of claim 10 wherein said activating unit ishoused in a non-heated region of said injection molding machine.
 12. Theinjection molding apparatus of claim 10 wherein the piston of saidcylinder is configured to engage an activating bar of said element,wherein said activating bar is in turn configured to engage said valvepin, such that a push-pull movement of the activating bar causes an upand down movement of said valve pin.
 13. The injection molding apparatusof claim 10 wherein said cylinder is configured to receive a signal fromthe injection molding machine to control the movement of said valve pin.14. The injection molding apparatus of claim 10 wherein said valve gateunit is one of several valve gate units, each valve gate unit having avalve pin, and wherein said slot in said activating bar is one ofseveral slots, each slot configured to engage one of said several valvepins.
 15. The injection molding apparatus of claim 10 wherein the shapeof said slot is configured to control the travel speed of said valvepin.
 16. The injection molding apparatus of claim 10 wherein saidactivating bar comprises more than one section.
 17. The injectionmolding apparatus of claim 16 wherein said activating bar comprises anactivating insert having a slot and a non-slotted connecting bar. 18.The injection molding apparatus of claim 17 wherein said activatinginsert and said connecting bar are configured to be connected withone-another using a tongue and groove arrangement.
 19. The injectionmolding apparatus of claim 10 wherein said activating bar is a one-pieceelement.